Oscilloscope

An oscilloscope (often abbreviated o'scope or scope) displays signal voltages as a 2-D graph, usually as voltage (vertical axis) as a function of time (horizontal axis).

The o'scope is one of the most important pieces of test equipment because it lets you look at what is happening in different parts of a circuit. Without it you are almost blind ( multimeters and logic analyzers can also help you "see" ).

The probe of a o'scope is held against, or is clipped to, the metal wire carrying the signal of interest.

A dual-trace o'scope has 2 probes, so 2 different signals can be seen -- so not only the shape of the signal can be seen, but also the exact time from events on one signal to events on the other signal.

Techniques

Sometimes one wants to look at a 8-bit data bus -- typically one uses a "logic analyzer" to look at lots of time-aligned digital signals.
For a given number of signals to look at, oscilloscopes (which show the true analog waveform) are much more expensive than logic analyzers (which only show if a digital waveform is hi or low, above or below the logic threshold).
Many people buy both a (dual-trace) o'scope and a 16-trace logic analyzer, which together have a total cost less than one true 8-trace o'scope.

... more techniques ...

Open Source Oscilloscopes

Of course, you have to already have a working o'scope in order to build and test another o'scope, making this the same sort of chicken-and-egg problem as the RepRap project, the GCC project, and other projects David Cary finds interesting.

XMEGA Xmegalab Development Kit and Oscilloscope

$249 The Xmegalab is a development board for AVR XMEGA microcontrollers, a dual channel oscilloscope, an arbitrary waveform generator and a scientific calculator. Xmegalab. Alpha version of the firmware (mostly in C) has been released under the GPL. Serial port; SD Card with FAT File System support, etc.

Xprotolab - Miniature Oscilloscope and Waveform Generator

$35 The Xprotolab is a small mixed signal oscilloscope in a DIP module, designed to be used on a breadboard. It also has an arbitrary waveform generator. Xprotolab.

Closed, COTS Hardware for PC Oscilloscopes

For low frequencies, pretty much any external sound card with a line input will work. External card line inputs generally have a range around 0-1 V whereas onboard microphone inputs only have up to about 50 mV, which just isn't enough sensitivity. The Virginia Tech Lab-in-a-Box recommends the Behringer UCA202. To use a sound card oscilloscope on a regular basis, a circuit with variable attenuation is recommended (i.e. 1x and 10x). Compensation for the hardware and software gain can be done as part of the attenuator circuit or in software.

PC Oscilloscope Software

Free Software

Sourceforge: xoscope is a digital oscilloscope for Linux that uses input from a sound card or EsounD and/or a ProbeScope/osziFOX and will soon support Bitscope hardware. The sound card device is hard-coded but instructions for modifying it are on the VTLUUG wiki.

Baudline GPL version is a signal analyzer designed for scientific visualization, using input from recorded data files or from a sound card. For Linux / Solaris. The source code is expensive and it is intended for qualified corporate or institutional buyers.

Miniscope v3 is a digital oscilloscope for Windows. It connects to device using external dll. Available libraries to connect with sound card, Microchip MCHPUSB Generic HID Demo and custom AT91SAM7S64 hardware.

Digital Soda is a simple GTK+ frontend for the DSO-2250 USB oscilloscope for Unix/Linux.

Osqoop is an open source software oscilloscope. Osqoop project features an arbitrary number of channels and long acquisition durations. Signal processing and external peripherals control is possible through a plugin architecture.

Non-PC Oscilloscope Projects

"Handheld Multifunction Scope" by Jingxi Zhang & Yang Zhang, 2007. "dual-channel oscilloscope supports 250 ksps for each channel". ... also: ohmmeter, capacitance meter, and inductance meter ... pulse generator ... small speaker and OLED output. All functions work stand-alone with OLED display, but it can also be to a host PC with the USB port to display waveforms on the PC display.

"The µSCOPE: A poorman's oscilloscope" by Ronald Dekker. An extremely small and low-cost circuit based on the 8 pin Microchip PIC12f675; displays "signals up to a few kHz" on a PAL TV screen. "isochronous code".

Epanorama has many links related to o'scopes and o'scope accessories [6].

Oscilloscope Design Discussions

some low-cost oscilloscopes

some low-cost oscilloscopes, in no particular order.
... it would be nice to mention sampling rate, # of analog input channels, # of digital input channels, whether it can be used under Linux, does it have output channels ... price should (?) include 2 analog probes, ... is it open hardware? ... anything else?

(about US$400.00) GAO2250 100MHz 250MS/s USB PC Oscilloscope, Gaotek Inc. A Canadian source for the DSO-2250. 2 input channels plus trigger. Provision for ground and calibration. Windows only, AFAIK, no Linux. Gao's latest website doesn't quote a price, but when I got mine it came to about CAN$500, including US conversion and Canadian taxes. [26]

Further Reading

External Links

"Scoping out palm-sized USB oscilloscopes" by Jack Ganssle 2005, Embedded Systems Design. A review of 3 USB oscilloscopes -- reader comments at the end mention a few more USB o'scopes. (FIXME: make sure all the scopes mentioned are included on the above list)